The Connection Process

To demonstrate how Bluetooth devices discover and connect with one another, let us use the scenario of a laptop connecting wirelessly to a mobile phone to use dial-up networking (DUN). This process is shown in Figure 6. Before any device can connect to another device, it has to initially look for devices that it might connect to. In Bluetooth, this is called the Inquiry Process. The inquiring device, which we call A, sends out an inquiry packet or repeated inquiry packets and waits to receive responses back. Discoverable devices in range respond to an inquiry by sending a Frequency Hop Synchronization (FHS) packet, which contains all the information device A needs to connect to the responding device, including the Bluetooth device's address, page scan modes, and clock offset. All devices that respond to the inquiry are reported to the host controller of device A. Whether or not the list of all devices discovered is presented to the user is application-dependent.

At this point, device A knows which devices are in range, but it does not yet know which devices support dial-up networking. Using the information retrieved from the inquiry process, device A now attempts to connect to the different devices that responded to its inquiry in order to find out what services they support. Depending on the application, device A may either 1) establish links to all the devices that responded to its inquiry and get the information about their services and later on reconnect with the one that supports dial-up networking; or 2) upon seeing that a device supports dial-up networking, directly proceed to setting up a connection with that device without finding out the services from the rest of the devices in the list. In Figure 6, the second option is adopted.

In order to find out the services of a device, device A sends out paging packets. A connectable device will respond and a baseband link can be established between the two devices. Following that, a L2CAP connection will be established before they can exchange service information. This information exchange is handled by the Service Discovery Protocol. Say a device B has responded that it has the dial-up networking service. A RFCOMM connection can then be established across the already existing L2CAP link. When this has been set, a dial-up networking connection can then be established on top of the RFCOMM connection, after which the laptop can then start using the cell phone to access the phone network without any cables being needed for connections.

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Conclusion

Bluetooth is a fast growing technology. More and more devices are coming out with Bluetooth capabilities built into the hardware and applications utilizing the Bluetooth technology are starting to come out as well. Although Bluetooth-enabled devices still cost considerably more than devices without Bluetooth capabilities, they do seem to be finding their niche in the market.

Parallel to market growth, Bluetooth is also undergoing continuous technical development. Even more profiles will be defined as new usage models emerge. There is also ongoing research into improving Bluetooth network performance, not only alongside other wireless networks, such as IEEE 802.11, but also among other Bluetooth networks as well. Furthermore, Bluetooth v2.0 is already under construction. Expected improvements from the current version include higher data rates and faster response times.

However, in order to become a widely accepted technology, several factors need to come into play. Being primarily a cable replacement technology, the price of enabling a device to use the Bluetooth technology should not cost significantly more than the cable it replaces. Furthermore, using Bluetooth should not be any more complicated than using cables. In particular, the connection process should be as seamless as plug and play technologies. Minimal configuration should be left to users and dependable service should be provided. This is certainly lacking in current Bluetooth solutions where a complicated set-up process and upnpredictable service has been known to frustrate potential users.

Another important driver for this technology will be killer applications. Many of the available Bluetooth hardware in the market today are already starting to address interoperability issues, which plagued early releases. However, applications available today are mostly single solutions such as wireless headsets for mobile phones and wireless keyboards, which usually work with only their targeted hardware. Users need to see integrated solutions and ones that deliver on the promise of interoperability. With applications that actually support the usage models, and single-chip solutions that actually meet the targeted $5 price (at high volumes), we might very well see Bluetooth in the mainstream.

Finally, regarding issues concerning the IEEE 802.11 network, the trend seems to be that both technologies are falling into their own categories. Bluetooth is emerging as the PAN technology as initially envisioned while IEEE 802.11 is settling into its WLAN category. In the near future, where users will be having a plethora of mobile devices around them, Bluetooth's inherent capabilities for handling high network loads while maintaining low-power operation and higher throughput might turn out highly valuable. However, peaceful co-existence between the two technologies will have to be addressed.